1. Field of the Invention
The present invention relates to a solid-state imaging device and a camera having the solid-state imaging device.
2. Description of the Related Art
An image sensor is a device which can be applied to various fields such as cameras or video recorders.
The image sensor used as such a device includes many pixels. The entire efficiency of the device is determined depending on a pixel size or a pixel structure.
In a color-image device, by disposing a solid-state absorption color filter material usually including organic materials in the pixels, the types of the pixels are divided into three colors of red, green, and blue.
To improve the efficiency of the pixels, a pixel-size lens is used as the uppermost element. Accordingly, by keeping incident light focused on a light-receiving element of each pixel and causing the pixel to capture the light incident on the pixel as much as possible, the light is caused not to diffuse into the neighboring pixels.
However, with the decrease in size of the camera, there is a need for further reducing the pixel size due to the restriction on optical elements such as camera lenses.
Since the decrease in pixel size reduces the light-receiving efficiency of the pixels and also reduces the volume of a photodiode, a decrease in peak gain of a pixel or a marked decrease in dynamic range of the camera is caused.
From such problems, there is a need for such a pixel design that an excellent response characteristic and a wide dynamic range are obtained under the same exposure conditions.
One method of improving the above-mentioned device is to increase the number of carriers resulting from one photon to more than one.
Some researchers suggested that an avalanche diode having a gain greater than or equal to 10 is used (for example, JP-T-2005-532696 and JP-A-9-331051 ([0006])).
This leads the device to have an excellent response characteristic and a wide response range even under a low light amount condition.